The present invention relates to reciprocating pumps, and in particular to various types of reciprocating pumps with a linear motor driver and to methods of pumping liquids with such reciprocating pump. Most preferably the pumps of this invention are hermetic reciprocating pumps and the methods of this invention are methods of pumping liquids with such hermetic pumps.
Reciprocating pumps are highly desirable for use in numerous applications, particularly in environments where liquid flow rate is low (e.g., less than 15 gpm) and the required liquid pressure rise is high (e.g., greater than 500 psi). For applications requiring less pressure rise and greater flow rate, single stage centrifugal pumps are favored because of their simplicity, low cost and low maintenance requirements. However, reciprocating pumps have a higher thermodynamic efficiency than centrifugal pumps by as much as 10% to 30%. Although reciprocating pumps are preferred for many applications, they are subject to certain drawbacks and limitations.
For example, traditional reciprocating pumps are commonly driven in a linear direction by a rotating drive mechanism through a slider-crank mechanism or other conventional mechanical mechanism for converting rotary motion to linear motion. These drive systems require multiple bearings, grease or oil lubrication, rotational speed reduction by belts or gears from the driver, flywheels for stabilization of speed, protective safety guards and other mechanical devices, all of which add complexity and cost to the pumps. Moreover, in these traditional constructions the stroke length of the piston is fixed, as is the motion of the piston over time (e.g., generally sinusoidal motion) during each cycle of operation. This results in a peak piston velocity near mid-stroke, which determines the peak Bernoulli effect pressure reduction and kinetic head loss pressure reduction in the fluid that enters the pump on the suction stroke of the piston, thereby effecting the net positive suction head (NPSH) requirement.
Pumps are subject to mechanical damage from insufficient NPSH. In particular, vaporization of liquid at the point of entry into the pump results in vapor bubble formation. Subsequent compression of the vaporized liquid causes violent collapse of the bubbles, resulting in the formation of sonic shock waves that ultimately can damage pump components. Therefore, it is important that the available NPSH of a pump installation be sufficiently above the required NPSH of the pump.
Pump designs requiring a low NPSH allow greater flexibility in installation, often reducing installation costs. In addition, a lower required NPSH assures a greater margin to cavitation and hence greater reliability in operation when inlet operating conditions are off-specification.
The NPSH requirement for reciprocating pumps is dictated by factors tending to reduce the local entry suction pressure, such as liquid line acceleration pressure drop and velocity induced pressure drop (Bernoulli effect and kinetic head losses) in the inlet line and inlet valve. The cylinder and piston size, as well as the inlet valve size and peak piston velocity are critical factors in setting the minimum required NPSH. In particular, larger cylinder, piston and inlet valve size allow a slower pump speed. This results in a lower NPSH requirement. As stated earlier, pump designs requiring a low NPSH allow greater flexibility in installation and also a greater margin to cavitation, both highly desirable attributes.
Adjustment of the speed of traditional reciprocating pumps to reduce the throughput (i.e., flow turndown) is limited largely by the size of the pump flywheel and the size of the electric motor driver. Traditional reciprocating pumps are typically operated at a fixed motor supply power alternating current (AC) frequency and thus a fixed nominal pump speed. Adjustment of the alternating current electrical supply frequency to the motor, such as by the use of a variable frequency drive, to reduce pump speed is typically limited in turndown to 50% of full design pump speed and flow rate. The function of the pump flywheel is to minimize speed fluctuation or ripple during each stroke cycle of the pump. This is accomplished by absorbing and releasing kinetic energy between the pump shaft and the flywheel during each cycle; resulting in a cyclic speed fluctuation of the pump slightly above and below the nominal speed. This is called speed ripple. Speed ripple results in greater and lesser amounts of motor torque at various portions of each pump stroke cycle. This fluctuating torque creates fluctuating motor current draw, which in the extreme can be detrimental to the motor by thermal overheating. The key factor in determining peak motor current draw is the percentage of speed fluctuation. It should be noted that for a given flywheel size and motor size, the speed ripple percentage increases by the square of the ratio of design speed to reduced speed. Additionally, as motor speed decreases, the ability of the motor fan to properly cool the motor decreases as well. These factors combine to create the practical 50% turndown limit. Special measures can be taken to reduce this limit, such as providing a separately powered motor cooling fan, significantly over sizing the pump motor frame or over sizing the pump flywheel. However, these special measures are expensive alternatives. Other means to achieve reduced pump speed, such as variable sheaf diameter belt systems or other mechanical speed ratio adjustment methods, suffer from problems of increased wear, slippage and excessive peak load failures.
When a greater operational flow turndown is required, traditional pumps generally are operated in a recycle mode or in a cyclic on/off mode with a hold up tank. Recycle flow around the pump can be extremely wasteful in pump power and adds cost and complication by requiring a recycle line, a recycle valve, a cooler and means for control. The use of a hold up tank also increases the expense of the system, requires significant excess space and complicates operation and maintenance of the pump system.
A further deficiency associated with traditional reciprocating pumps resides in the need to provide an effective seal between the piston and the pump cylinder. Such a seal typically is provided by piston ring dynamic seals. However, even with the provision of such seals, some leakage is typically encountered, and in many applications represents a nuisance for disposing or recycling of the leaked material.
In traditional reciprocating pumps, piston ring wear is often the primary cause of pump repair maintenance. This results, in part, from sealing the full differential pressure between the pump discharge pressure and the piston backside leakage collection pressure, thereby causing these seals to wear quickly. Specifically, the backside pressure often is equal to or less than the pump inlet pressure, thereby creating a very significant pressure drop across the piston ring seals. This, in turn, increases the resulting piston ring wear rate.
Inlet and outlet valves on a reciprocating pump are typically fluid-activated check valves of specialty design to accommodate the high cyclic rate of the pump while achieving the longest possible operating life. Still, even with the specialty design of these valves, valve failure is often the reason for a pump malfunction. The design speed of the reciprocating pump is based on the required volumetric flow rate and the swept volume of the piston in the pump cylinder. Because a larger swept volume operating at a slower speed requires a larger physical pump size and a higher capital cost, it has been the practice to install a small pump operating at the highest speed permissible, as limited by reciprocating forces, piston ring wear rates and NPSH requirements. Such high speeds, typically in the range of 200 to 600 rpm, place a heavy burden on valve life.
It is desired to have a reciprocating pump that does not have the aforementioned drawbacks of traditional reciprocating pumps, and to actually enhance the positive aspects associated with traditional reciprocating pumps. The reciprocating pumps of the present invention minimize or eliminate traditional reciprocating design drawbacks, including: (1) maintenance of wearing parts, such as valves, piston rings and rod packings; (2) maintenance due to pump cavitation damage in low NPSH applications; (3) leakage of the pumped fluid from the process stream; (4) leakage of the pumped fluid to the pump surroundings; (5) high NPSH requirements for installation design; (6) lubrication contamination of the pumped liquid and pump surroundings; (7) high capital cost; (8) space requirements for installation and (9) hazards associated with exposed moving parts. With the present invention, the aforementioned drawbacks are either minimized or eliminated, while enhancing the positive features of traditional reciprocating pumps, such as high thermodynamic efficiency.
Beneficial aspects of the reciprocating pumps of the present invention that have not heretofore been available include: (1) variable flow from 0% to 100% of design flow rate at full design pressure, with improved efficiency; (2) lower heat leak in cold standby for cryogenic liquid pumping applications; and (3) increased output pressure capability at reduced speed.
Prior art attempts to improve the performance of reciprocating pumps have focused in three (3) areas; namely, modifying the size of traditional slider crank-driven reciprocating pumps, innovative developments in reciprocating cryogenic and/or hermetic pump designs, and converting to linear motor powered reciprocating designs.
With respect to modifying the sizing of traditional slider crank-driven reciprocating pumps, attempts have been made to increase the pump size to provide a swept volume greater than is conventionally considered to be necessary. Employing a bigger pump increases pump costs, but with the benefits of reducing wear-part maintenance by reducing the number of pump cycles required to deliver a predetermined flow, reducing maintenance costs resulting from insufficient NPSH damage, reducing installation costs to meet a high NPSH requirement (e.g., less tank elevation required), and increasing thermodynamic efficiency due to lower speed operation and reduced inlet and outlet valve pressure drop losses.
However, the above stated gains resulting from the use of a larger pump are achieved at the significant expense of: (1) higher pump capital cost; (2) increased fluid leakage from the pumped stream due to the larger piston diameter required to be sealed; (3) increased fluid leakage to the pump surroundings resulting from the larger diameter of the required rod seal; (4) increased general installation costs due to the use of larger-sized parts; (5) increased space requirements due to the use of larger sized parts; (6) increased cost of spare parts; and (7) increased cost of residual maintenance labor due to larger size and handling.
The balancing of the benefits and deficiencies enumerated above has generally resulted in a limitation on the extent of over sizing of reciprocating pumps.
Developments in cryogenic reciprocating pumps have included: (1) employing new dynamic seals, as disclosed in U.S. Pat. No. 4,792,289; (2) modifying the inlet and/or outlet valve designs, as disclosed in U.S. Pat. Nos. 4,792,289; 5,511,955 and 5,575,626; (3) reduced heat leak designs, as disclosed in U.S. Pat. Nos. 4,396,362 and 4,396,354; (4) introducing a second (or multiple) pre-compression chamber(s) for reduced NPSH requirement, as disclosed in U.S. Pat. Nos. 4,239,460; 5,511,955 and 5,575,626; and (5) introducing sub-cooling mechanisms for reducing the NPSH requirement and providing improved volumetric efficiency, as disclosed in U.S. Pat. Nos. 4,396,362; 4,396,354 and 5,511,955. However, none of the above enumerated improvements employ a hermetic design (i.e., no dynamic seals for the pumped liquid to prevent leakage to the ambient surroundings of the pumps).
U.S. Pat. No. 4,365,942 discloses a hermetic cryogenic pump including electrical coils that are maintained superconductive by virtue of the extreme cold temperature of the liquid helium to be pumped. While this design may be unique to the characteristics of liquid helium, it is not widely applicable for use in pumping other fluids.
As noted earlier, other prior art has suggested the use of a linear motor as a driver for a reciprocating pump. Application of this type of driver to a pump has suggested benefits in achieving compact size, reduction of power consumption, reduction of cost, reduction of maintenance and application to situations previously impossible to achieve with traditionally driven pump designs. The use of such linear motor drivers has proven to be applicable to both hermetic and non-hermetic pump designs. Linear motor-powered pumps have been disclosed for use in the down-hole pumping of oil and water, as disclosed in U.S. Pat. Nos. 4,350,478; 4,687,054; 5,179,306; 5,252,043; 5,409,356 and 5,734,209.
U.S. Pat. No. 4,687,054 discloses a wet air gap design that does not employ seals to separate the pumped liquid from the motor""s air-gap between the stator and the armature.
U.S. Pat. Nos. 4,350,478; 5,179,306; 5,252,043 and 5,734,209 disclose the use of seals for protecting the motor air-gap from the pumped liquid. Many of the prior art seal designs have the air-gap filled with a lubricating and heat transfer oil. It should be recognized that virtually all of the aforementioned pumps operate fully submerged in the liquid that they pump, and therefore, achieving a hermetic seal to prevent leakage to their ambient surroundings, as desired in the preferred embodiments of the present invention, is a moot point.
Other electric linear motor-driven pumps employing a hermetic design have been disclosed for use in a number of applications, such as for blood pumping (U.S. Pat. No. 4,334,180), large volume, low pressure gas transfer applications (U.S. Pat. No. 4,518,317), a conceptual double-acting pump design (U.S. Pat. No. 4,965,864) and non- hermetic designs employing conventional flat face linear motors (U.S. Pat. No. 5,083,905).
None of the aforementioned prior art teaches a hermetic pump design for intended industrial processes or product delivery applications having all of the benefits of the present invention.
As utilized throughout this application to describe the various embodiments of the invention, the term xe2x80x9cswept volumexe2x80x9d in reference to the dispensing chamber and/or the reservoir chamber, or in reference to the movement of the piston assembly, refers to the incremental change in volumes of the fluid-receiving regions of the dispensing chamber and reservoir chamber caused by movement of the piston assembly through either a dispensing stroke or a suction stroke. During the dispensing stroke of the piston assembly the volume of the fluid region of the dispensing chamber incrementally decreases by substantially the same amount that the volume of the fluid region of the reservoir chamber increases. During the suction stroke of the piston assembly the volume of the fluid region of the reservoir chamber incrementally decreases by substantially the same amount that the volume of the fluid region of the dispensing chamber increases. The above-discussed incremental decreases and increases in volume of the fluid regions of the dispensing chamber and reservoir chamber are equal to the incremental change in volume of the piston assembly within the dispensing chamber and reservoir chamber as the piston assembly moves through its dispensing stroke and suction stroke, respectively. When the sealing member between the cylinder and piston assembly is fixed against movement to the cylinder, the swept volume equals the traveled distance of the piston assembly moving through the sealing member (in either the dispensing or suction strokes) times (x) the cross-sectional area of that length of the piston assembly which passes through the sealing member.
Reference to xe2x80x9chermeticxe2x80x9d or xe2x80x9chermetically sealedxe2x80x9d in referring to the various pumps of this invention means pumps that are free of dynamic seals between the pumped fluid and the ambient surroundings of the pump. Dynamic seals are those seals between bodies that move relative to each other with a resulting sliding motion at the sealing point and function to prevent egress of a fluid from a pressurized area to an area of lesser pressure. As stated above, no such dynamic seals are included in hermetic pumps within the scope of this invention between the pumped fluid and the ambient surroundings of the pump.
Reciprocating pumps for liquids include a cylinder having outer walls that provide a closed interior compartment having opposed ends. A piston assembly has a dispensing end and an opposed end, and this assembly is moveably mounted within the compartment for movement in opposed linear directions between the opposed ends of said compartment. A sealing member is provided between the piston assembly and the piston cylinder to maintain a dynamic fluid seal between the piston assembly and piston cylinder as the piston assembly moves within the closed interior compartment of the cylinder. The sealing member separates the interior compartment into a dispensing chamber and a reservoir chamber. A linear magnetic drive generates a linearly moving magnetic field for moving the piston assembly in opposed linear directions. A valve controlled inlet conduit communicates with the dispensing chamber of the interior compartment for directing liquid into the dispensing chamber to fill the volume of the dispensing chamber as the piston assembly moves through a swept volume in one linear direction through a liquid-receiving suction stroke. A valve controlled outlet conduit communicates with the dispensing chamber of the interior compartment for directing pumped liquid out of the dispensing chamber as the piston assembly is moved through the swept volume in a direction opposed to said one linear direction through a liquid dispensing stroke. An energy storage and release media cooperates with the piston assembly for storing energy as a result of the movement of the piston assembly through the suction stroke and for releasing the stored energy to said piston assembly as the piston assembly is moved through the dispensing stroke.
In the preferred embodiments of this invention, the pumps are hermetic pumps.
In a preferred embodiment of the invention, the energy storage and release media at least partially fills the reservoir chamber for storing energy therein as the piston assembly is moved through a swept volume of the reservoir chamber during the suction stroke of said piston assembly.
In the most preferred embodiments of this invention, the energy storage and release media are subject to elastic compression or expansion to store and release energy. Most preferably the energy storage and release media is a gaseous substance. When a gaseous substance is employed as the energy storage and release media it preferably at least partially fills the reservoir chamber of the cylinder. However, within the broadest aspects of this invention, liquid can be included in the reservoir chamber at a level such that that portion of the piston assembly in the reservoir chamber is completely within liquid. In fact, in certain embodiments of this invention the liquid can completely fill the reservoir chamber.
In a preferred embodiment of the invention, the magnetic drive is a poly-phase linear motor including an electronic power supply and a programmable microprocessor for controlling the operation of the power supply to adjustably control movement of the piston assembly.
Most preferably, the programmable microprocessor can adjustably control the operation of the power supply to adjustably control the characteristics of piston assembly motion such as the length of stroke of the piston assembly in each linear direction, the time period of such motion in each linear direction, the cyclic rate of reciprocation of the piston assembly and specifically the position, velocity and acceleration of the piston assembly throughout the entire path of movement of the assembly in the opposed linear directions, at every point in time of that cyclic motion. In addition, piston assembly motion can be controlled to include variable time length periods in which no motion is taking place. These periods of no motion can occur at any time or location within any cycle, or between cycles, as desired.
In one preferred form of the invention, the programmable microprocessor adjustably controls the time duration of each stroke of the piston assembly (e.g., the suction stroke and dispensing stroke) so that the time duration of one stroke (e.g., the suction stroke) is different from the time duration of the other stroke (e.g., the dispensing stroke). In a preferred manner of operating the pump the suction stroke is of a longer time duration than the dispensing stroke.
In another preferred form of the invention, the programmable microprocessor adjustably controls the cyclic movement of the piston assembly so that it either is continuous or discontinuous. That is, the operation of the pump can be controlled so that a pause in motion of any desired time duration is provided at any one of various locations within any cycle of the piston assembly, or between successive cycles of the piston assembly; each cycle including one suction stroke and one dispensing stroke.
In a preferred embodiment of this invention, the piston includes a position sensor that provides an electrical feedback signal to the programmable microprocessor of the magnetic drive system.
In the most preferred embodiment of this invention, the linear magnetic drive includes a stator and armature, with the stator being located adjacent and outside of the pump cylinder and the armature being located on the piston assembly inside of the cylinder.
In a preferred embodiment of the invention, wherein the energy storage and release media is a gaseous substance, an additional mechanical energy storage and release media (e.g., a spring, bellows, etc.) can be employed for assisting in the storage of energy derived from motion of the piston assembly in one linear direction and for releasing, or imparting, the stored energy to the piston assembly during subsequent motion of the piston assembly in a linear direction opposed to one said linear direction.
In a preferred embodiment of this invention, a liquid sump is provided in communication with a valve-controlled inlet conduit for supplying liquid to the pump.
Most preferably, when a liquid sump is provided it is partially filled with the liquid to be pumped and includes a ullage space with an elastic compressible and expansible media (e.g., a gas) therein to minimize pulsation of liquid flow to the pump (i.e., permit delivery of liquid to the sump at a substantially constant flow rate) in spite of the fact that the liquid being drawn into the pump is at a non-constant, pulsating flow rate.
For some applications, the ullage space includes a thermal anti-convection and anti-conduction insulator material, and, optionally, a thermally conductive element is provided for assisting in maintaining the surface of the liquid in the sump at a desired elevation.
Most preferably, the sump includes a vent line, a valve and liquid float for operating the valve to maintain the liquid in the sump at a desired elevation.
In the preferred embodiment of the invention, a conduit is provided for connecting the discharge from the pump to a bottom wall section of the sump through a removable and sealed connection.
In another embodiment of the invention, a conduit is provided for connecting the discharge from the pump through the sump ullage space.
In accordance with this invention, the liquid sump can be completely filled with the liquid being pumped so as to eliminate any ullage space for receiving an elastic and expansible media. In this embodiment of the invention, an additional elastic compressible and extensible media, e.g., a liquid-filled flexible bellows or diaphragm accumulator, is maintained in communication with the interior of the sump to minimize pulsation of liquid delivered to the sump, i.e., provide for a substantially constant flow rate of liquid into the sump.
In certain embodiments of this invention, the gas constituting the energy storage and release media in the reservoir chamber of the pump interior compartment is non-condensible, and is not a vapor of the liquid being pumped, and the pump includes means for supplying and discharging controlled amounts of the non-condensible gas to the pump.
In other embodiments, the gas constituting the energy storage and release media in the reservoir chamber of the pump interior compartment is partially composed of vapor of the liquid being pumped and partially composed of a non-condensible gas that is not a vapor of the liquid being pumped, and the pump includes means for supplying and discharging controlled amounts of said non-condensible gas to the pump. For some applications, the gas can be composed solely of the vapor of the liquid being pumped.
In a preferred embodiment of the invention, the pump is employed for pumping a liquefied gas, which may be a cryogenically liquified gas, and the cylinder includes heat-insulating means in the region of the dispensing chamber to maintain the liquid at a desired, cold temperature, and heating means in the region of the reservoir chamber to maintain the gas in this latter region at a desired warm temperature and the pressure of the gas in the region of the reservoir chamber is maintained below the critical pressure of the gas. However, it should be understood that in accordance with the broadest aspects of this invention the pumps can be operated with the pressure of the gas in the reservoir chamber at or above the critical pressure of the gas.
In another embodiment of this invention, the reservoir chamber of the pump chamber includes a bellows section therein, and the energy storage and release media communicates with the bellows section such that the bellows sections is moved in response to the suction stroke of the piston assembly to store energy in said energy storage and release media.
In a preferred embodiment of the invention, the bellows section is an end section of the reservoir chamber and the energy storage and release media (e.g., a spring) engages an outer wall of the bellows section. In this embodiment the bellows section of the reservoir chamber can be filled with a liquid.
In a preferred embodiment of this invention a bellows member is located in the reservoir chamber and the energy storage and release media is a gaseous substance filling said bellows section.
A method for pumping a liquid in accordance with this invention includes the steps of providing a pump having a piston assembly mounted for reciprocating movement in a closed interior compartment of a piston cylinder having opposed closed ends, the piston assembly including a dispensing end and an opposed end; generating a linearly moving magnetic field for reciprocating the piston assembly within the cylinder through a dispensing stroke and a suction stroke, respectively; providing a sealing member between the piston assembly and piston cylinder to maintain a dynamic fluid seal between the piston assembly and piston cylinder during the dispensing and return strokes of said piston assembly, said seal dividing the interior compartment into a dispensing chamber and a reservoir chamber; introducing liquid to be pumped into the dispensing chamber; maintaining the liquid in the cylinder at a level such that a lower surface of the sealing member and the dispensing end of the piston assembly are maintained within the liquid throughout the length of the dispensing and suction strokes of the piston assembly and providing an energy storage and release media in a location for storing energy when the piston assembly is moved through the suction stroke and for imparting the stored energy to the piston assembly as the piston assembly is moved through the dispensing stroke.
In accordance with the preferred method of this invention, the energy storage and release media is provided in the reservoir chamber of the interior compartment.
In accordance with a preferred method of this invention, the energy storage and release media is a gaseous substance, and most preferably fills the reservoir chamber to a level such that the opposed end of the piston assembly (i e., the end opposite the dispensing end) is in the gaseous volume during the entire dispensing and suction strokes of the piston assembly.
In the preferred method including a gaseous substance as the energy storage and release media, a liquid/vapor interface between the liquid to be dispensed and the gaseous substance is established and maintained at an elevation in which the sealing member is fully submerged within the liquid during the operation of the pump.
In accordance with the preferred methods of this invention, the step of generating the linearly moving magnetic field is provided by an electronic power supply controlled by a programmable microprocessor.
A preferred method of this invention includes the steps of determining the position of the piston assembly within the cylinder and controlling the linearly moving magnetic field in response to that determination.
A preferred method of this invention includes the steps of generating the linearly moving magnetic field with a linear magnetic drive employing a stator and armature, with the stator being located adjacent and outside of the piston cylinder of the pump and the armature being located on the piston assembly inside the piston cylinder to thereby create an air-gap between the inner surface of the stator and the outer surface of the armature in which the outer wall of the piston cylinder is disposed.
A preferred method of this invention includes the step of employing both a gaseous substance and an additional mechanical media for storing energy derived from motion of the piston assembly in either the dispensing stroke or the suction stroke, and then imparting the stored energy to the piston assembly during the other stroke of the piston assembly.
In accordance with one method of this invention, the gaseous substance in the reservoir chamber is non-condensible and is not a vapor of the liquid being pumped, and the method includes the steps of supplying and discharging controlled amounts of non-condensible gas to the pump.
In accordance with one method of this invention, the gaseous substance in the reservoir chamber is a vapor of the liquid being pumped.
In accordance with another aspect of the method of this invention, the gaseous substance in the reservoir chamber is partially composed of vapor from the liquid being pumped and is partially composed of a non-condensible gas that is not a vapor of the liquid being pumped, and this method includes the steps of supplying and discharging controlled amounts of non-condensible gas to the pump.
A preferred method of this invention includes the step of modulating the linearly moving magnetic field during the pumping operation to vary the motion of the piston assembly.
The preferred method of varying the motion of the piston assembly includes the step of varying one or more of the length of stroke of the piston assembly, the cyclic rate of reciprocation of the piston assembly, the position of the piston assembly, the velocity of the piston assembly and the acceleration of the piston assembly.
A preferred method of this invention includes the step of providing liquid to be pumped into the piston cylinder from a liquid sump. Most preferably, in this embodiment of the invention, the method includes the step of maintaining the liquid level in the sump at a desired elevation.
A preferred method of this invention in which a liquid sump is employed includes the step of only partially filling the sump with the liquid to be pumped and including a compressible media in the ullage space within the sump.
In accordance with another aspect of the method of this invention, the sump is substantially completely filled with a liquid to be dispensed and an accumulator, e.g., a flexible bellows or diaphragm, or other media is provided for minimizing the flow pulsation of liquid being directed into the sump.
A preferred method of this invention includes the step of insulating the cylinder of the pump in a region of the dispensing chamber to maintain the liquid to be pumped at a desired cold temperature and heating a region of the reservoir chamber to maintain said region of said reservoir chamber at a desired warm temperature to maintain at least a portion of the reservoir chamber volume in a gaseous state. Most preferably the pressure of the gas in the reservoir chamber is maintained below the critical pressure of the gas; however, it is within the broadest aspects of this invention to operate with the gas pressure at or above the critical pressure of the gas. This method is particularly useful in the pumping of liquefied gas, and more particularly, cryogenically liquefied gas.
In accordance with one method of this invention, a bellows section is provided in said reservoir chamber in communication with energy storage and release media such that movement of the piston assembly through the suction stroke moves the bellows section to store energy in the energy storage and release media.
In a preferred form of this latter method, the bellows section is an end section of the reservoir chamber and the energy storage and release media (e.g., a spring) communicates with said bellows section. In this embodiment of the invention the bellows section can be completely filled with a liquid.
In one embodiment of a method in accordance with this invention, the bellows section is located inside the reservoir chamber and is filled with a gaseous substance, said gaseous substance being said energy storage and release media.